1) Field of the Invention
The present invention relates to a multilayered laminate based on polyethylene, vessels made thereof and a resin composition to be used for such laminate as well as a resin composition obtained as a regrind from such laminate or vessel.
2) Related Techniques
A polyolefin, for example, polyethylene, has been used for producing many articles including various vessels due to its superior properties, such as strength, shock resistance, heat resistance etc. For gasoline containers, however, due to an insufficient ability of a polyolefin resin for barriering against gasoline, it has been practised to use polyolefin resin in combination with another resin exhibiting superior ability for barriering against gasoline, such as an ethylene/vinyl alcohol copolymer or a polyamide resin.
Bottles made of a multilayered plastic laminate composed of, for example, a layer of an ethylene/vinyl alcohol copolymer which is superior in the barriering ability against gasoline and a layer of a polyethylene which is superior in the strength and shock resistance, have found their wide uses for, such as smaller containers for agricultural chemicals and larger tanks for gasoline for automobiles. For such a multilayer construction, an adhesive layer is interposed between the polyethylene layer and the ethylene/vinyl alcohol copolymer layer, in order to increase the interlayer adhesion between them.
A multilayer blow molding for producing such a bottle suffers, in general, from occurrence of scraps and flashes amounting to about 30-40 wt.-% of the through-put and, therefore, a reclamation and reuse thereof is unavoidable in the economical point of view. Thus, an additional component layer made of a so-called "regrind" resulting from re-grinding or crushing such scraps and flashes may be employed in particular for the laminate construction. The regrind is made of a ternary mixture of a polyethylene, an ethylene/vinyl alcohol copolymer and an adhesive resin and may cause a deterioration in the appearance and mechanical strengths, such as an impact strength etc., of the resulting product, since the compatibility of a polyethylene with an ethylene/vinyl alcohol copolymer is, in general, poor. For this reason, the regrind-containing layer of prior art is made of a resin composition containing the regrind under dilution by a fresh polyethylene up to such a dilution proportion that would cause no deterioration of the material properties, so that the prior art has only an insufficient contribution to the effective utilization of regrind.
The adhesive layer plays here some role as a "compatibilizer" for improving the compatibility of the polyethylene with the ethylene/vinyl alcohol copolymer, nevertheless, the ability for improving the shock resistance by an adhesive resin of prior art has been insufficient.
Many formulations have been proposed in the past for a regrind comprising a polyolefin and an ethylene/vinyl alcohol copolymer. For example, Japanese Patent Kokais Sho 60-240429 A (corresponding to U.S. Pat. No. 4,629,596), Sho 62-11748 A, Hei 2-261863 A, Hei 3-180341 A and Hei 5-125232 A give various proposals for improving the performances of regrinds comprising a polyolefin and an ethylene/vinyl alcohol copolymer. These prior arts have aimed at an improvement in the stabilization of operation of the process or in the adhesion strength onto the ethylene/vinyl alcohol copolymer, which is different from what is contemplated by the present invention.
Japanese Patent Kokai Sho 57-11052 A discloses a laminate composed of a lamination of (a polyethylene layer)/(a layer of a regrind composed of a polyethylene and an ethylene-vinyl alcohol copolymer)/(a layer of an ethylene-vinyl alcohol copolymer). The compositions of the polyethylene and of the modified polyethylene used in this prior art are not clear by the disclosure of this patent gazette and, in addition, it is intended by this prior art to prevent the interlayer exfoliation and to improve the moldability and the appearance of the molded product. There is in this patent gazette no suggestion as to the resin composition providing for a superior shock resistance such as that according to the present invention. Japanese Patent Kokai Hei 3-72539 A discloses a regrind composition containing a polyethylene and an ethylene/vinyl alcohol copolymer, which discloses, however, only a technique of using a special ethylene/vinyl alcohol copolymer. Japanese Patent Kokai Hei 3-227346 A also discloses a regrind composition containing a polyethylene and an ethylene/vinyl alcohol copolymer, in which, however, only resin compositions having a content of ethylene/vinyl alcohol copolymer of 50% by weight or more are disclosed.
In the past, it has commonly been accepted that the impact strength of a polyethylene resin containing an ethylene/vinyl alcohol copolymer should be decreased by the content of the ethylene/vinyl alcohol copolymer, since this is a foreign matter to polyethylene. However, it was discovered by the inventors from their sound researches for improving the impact strength of such a polyethylene resin of a resin composition containing an ethylene/vinyl alcohol copolymer, that a resin composition based on polyethylene which comprises a high density polyethylene as the main component and which has a specific melt flow rate and a specific density and contains an ethylene/vinyl alcohol copolymer and a modified ethylene/.alpha.-olefin copolymer having a specific melt flow rate and a specific density and modified by being grafted thereon with an unsaturated carboxylic acid or its derivative may bring about a resin exhibiting a high impact strength comparable to that of an ethylene homopolymer and, therefore, can be recycled, whereby the present invention has been reached.